Understanding IPv6 Link-local Addresses Zone IDs

by George Chetcuti [Published on 8 July 2011 / Last Updated on 8 July 2011]

As we have noted in a previous post all IPv6 Link-local Addresses (LLA) share the same network identifier (fe80::) hence, you can cannot determine which interface an LLA is bound to, if the computer has multiple network adapters connected to different network segments. In fact, it distinguishes the networks by using a numeric zone ID, following a percent sign after the IP address as shown below:
Fe80::4432:34d6:e6e6:b122%1
Fe80::4d3d:3426:46e6:1457%2
The two characters after each address indicate that the preceding networks are connected to the zone IDs 1 and 2 respectively. Zone IDs can be used with other types of addresses but it is recommended to always use the zone ID when connecting to LLAs.
An important fact to remember is that zone IDs are relative to the sending host. For instance, if you want to ping another computer's LLA you have to specify your computer's network adapter zone ID at the end of the target computer IP address. For example, in the command ping fe80::4d3d:3426:46e6:1457%2, the address is of the computer you want to ping while the zone ID (%2) corresponds to the network interface of your computer.
In Windows Servers 2008 the zone ID for an LLA is assigned on the basis of a parameter called the interface index for that network interface. You can view a list of interface indexes on a computer by typing netsh interface ipv6 show interface at a command prompt.

As we have noted in a previous post all IPv6 Link-local Addresses (LLA) share the same network identifier (fe80::) hence, you can cannot determine which interface an LLA is bound to, if the computer has multiple network adapters connected to different network segments. In fact, it distinguishes the networks by using a numeric zone ID, following a percent sign after the IP address as shown below:

Fe80::4432:34d6:e6e6:b122%1

Fe80::4d3d:3426:46e6:1457%2

The two characters after each address indicate that the preceding networks are connected to the zone IDs 1 and 2 respectively. Zone IDs can be used with other types of addresses but it is recommended to always use the zone ID when connecting to LLAs.

An important fact to remember is that zone IDs are relative to the sending host. For instance, if you want to ping another computer's LLA you have to specify your computer's network adapter zone ID at the end of the target computer IP address. For example, in the command ping fe80::4d3d:3426:46e6:1457%2, the address is of the computer you want to ping while the zone ID (%2) corresponds to the network interface of your computer.

In Windows Servers 2008 the zone ID for an LLA is assigned on the basis of a parameter called the interface index for that network interface. You can view a list of interface indexes on a computer by typing netsh interface ipv6 show interface at a command prompt.

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